Measurements of surface elastic torques in liquid crystals : a method to measure elastic constants and anchoring energies

2014 Surface torques exerted by a nematic liquid crystal on a solid plate are investigated. Three different geometries are considered. The torques are generated by applying a uniform magnetic field to the nematic sample and are measured by a torsion pendulum. The elastic constants of the nematic Liquid Crystal and the anchoring energy at the interface can be obtained by this kind of measurements. As a main advantage of this technique, the measurements of the elastic constants are poorly sensitive to small misalignments of the director and are not affected from a finite value of the anchoring energy. Experimental results for the splay and bend elastic constants of the nematic LC 4-pentyl-4’-cyanobiphenyl (5CB) are given and compared with previous experimental results. Revue Phys. Appl. 21 (1986) JUILLET 1986 PAGE 451